1. Field of the Invention
The present invention relates to a solid-state imaging device, which includes plural dedicated imaging pixels and plural phase difference detection pixels and performs automatic focusing of phase difference method based on an image obtained from the phase difference detection pixel.
2. Description of the Related Arts
Digital cameras, which comprise solid-state imaging device such as a CCD image sensor or a CMOS image sensor and produce a digital image, become widespread. Most of the digital cameras include an autofocus (AF) function to automatically regulate the focus of an imaging lens, and as the AF function, a contrast detection method is widely adopted. Since it is not necessary to additionally provide a dedicated sensor for measuring a distance to a subject or a solid-state imaging device for AF, the contrast detection method has an advantage that the AF function can be realized with relatively low cost.
However, since a focus lens needs to move to obtain a plurality of contrast evaluation values, the contrast detection method has a problem that it takes longer time for focusing in comparison with other methods.
To solve this problem, in Japanese Patent Laid-Open Publication No. 2004-361611, a convex section and a concave section are formed on an imaging surface of the solid-state imaging device, and a photoelectric conversion element for AF is provided on each of the convex section and the concave section. In this configuration, since whether the focus is shifted forwardly or backwardly can be judged from one image capturing by comparing contrast evaluation values of the photoelectric conversion element for AF on the convex section and that on the concave section, a movement range (a search range) of the focus lens becomes narrower, and AF processing becomes of high-speed.
However, in the configuration of Japanese Patent Laid-Open Publication No. 2004-361611, since the focus lens must move in the movement range although which can become narrower, speedup of the AF processing has a limit. For the digital camera, improvement of functions and a low-price policy is progressing, so it is wished that the AF processing could be performed faster without causing increase in cost.
To meet such a demand, a solid-state imaging device for phase difference AF which can perform focus detection by one image capturing is suggested in Japanese Patent No. 2959142 and so on. The solid-state imaging device for phase difference AF comprises a plurality of first pixels in which a microlens is disposed such that an optical axis of the microlens is shifted from the center position of a light receiving surface of a photodiode (PD), and a plurality of second pixels in which a microlens is disposed such that an optical axis of the microlens is shifted the same distance in a direction opposite to the first pixel from the center position of the light receiving surface of the PD.
In the solid-state imaging device for phase difference AF, depending on a shift direction of the microlens, the first pixel and the second pixel have selectivity to an angle of each incident light. When the solid-state imaging device for phase difference AF is applied to the imaging apparatuses such as digital cameras, depending on a focusing state of the imaging lens of the digital camera, displacement (a phase difference) occurs between an image composed by each first pixel and an image composed by each second pixel. A displacement direction and a displacement amount of each image correspond to a displacement direction and a displacement amount of a focus of the imaging lens. Each image accords when the imaging lens becomes in-focus, and a displacement amount becomes the larger when a focus is shifted the farther. Therefore, in the solid-state imaging device for phase difference AF, a focus adjustment quantity of the imaging lens can be calculated by detecting the displacement amount and the displacement direction of the image composed by each first pixel and the image composed by each second pixel.
Accordingly, when the solid-state imaging device for phase difference AF is used, since It is not necessary to move the focus lens, it can perform AF in higher-speed than that of the contrast detection method. In addition, like the contrast detection method, since it is not necessary to provide a dedicated sensor, a solid-state imaging device for AF and so on, there is no increase in cost.
In the first pixel and the second pixel, since it is necessary to shift the optical axis of the microlens from the center position of the light receiving surface of the PD, the microlens needs to be small, and light receiving sensitivity at the time of image capturing becomes the lower than a normal pixel as the microlens becomes the smaller. Therefore, in the solid-state imaging device for phase difference AF, the dedicated imaging pixel consisting of the normal pixel is provided in addition to the phase difference detection pixel consisting of the first pixel and the second pixel, phase difference AF is performed with the phase difference detection pixel, and image capturing of a subject is performed with the dedicated imaging pixel.
However, when the imaging surface is constituted of an arrangement of the phase difference detection pixels and the dedicated imaging pixels, it has a problem that a light receiving amount of the dedicated imaging pixel becomes high at a position adjacent to the phase difference detection pixel. Since the microlens of the phase difference detection pixel is small, at the position where the phase difference detection pixel and the dedicated imaging pixel are next to each other, a gap between the microlenses becomes larger in comparison with the position where the dedicated imaging pixels are next to each other. The increase of the light receiving amount of the dedicated imaging pixel adjacent to the phase difference detection pixel is caused because the PD of the dedicated imaging pixel receives light incident from this gap.
The increase of the light receiving amount of the dedicated imaging pixel as the above appears as a noise on a captured image. To suppress this noise, the increase of the light receiving amount of the dedicated imaging pixel adjacent to the phase difference detection pixel may be corrected when the captured image is formed. However, when the correction process is executed, additional time will be required for imaging. Therefore, it is wished that the solid-state imaging device for phase difference AF is constituted so that light of uniform quantity is incident on the PD of each dedicated imaging pixel.